In the field of safety system design for vessels under positive pressure relative to the atmosphere, devices to relieve excess pressure are desirable for safety purposes. Excessive pressurization may be caused by an emergency such as a loss of power, a loss of reactor cooling water, and/or a fire surrounding a reaction vessel and heating the fluids therein. Likewise, heat may be generated for example by a runaway chemical reaction within a vessel. In the case of a catalyzed chemical reaction, catalyst activity levels have increased over the years through research and development, and the risk of such runaway reactions and safety concerns related thereto has increased.
Safety relief systems are typically provided for an emergency vent in a pressure vessel and are sized according to expected over pressurizations due to an emergency to quickly and safely relieve excessive system pressure without rupturing the pressurized vessel. The American Society of Mechanical Engineers (ASME) states that safety and protection relief systems cannot be electrically driven, so that they will operate in the event of a power failure. Examples of such ASME safety relief systems include mechanical relief valves, rupture disks, etc. However, activation of traditional relief systems may have an adverse environmental impact and/or may require significant maintenance work and loss of production time to bring the vessel back to service. Therefore, a common practice in the industry is to install an Engineered Control System (ECS) to prevent the pressure to reach the relief set point. Such practices as early relief, depressurization, dumping, etc are typically employed. For a reactor vessel, injection of a kill agent at the onset of a runaway to stop the reaction is normally used. However, the reliability of a reactor “kill” system depends upon the availability of external energy sources. A typical reactor kill system requires electricity to power a control system including an instrument signal, programmed logic interlock, electrical solenoids, etc. It also requires the availability of pneumatic power (i.e. instrument air) to drive the valves' actuators. In certain emergency scenario, i.e. power failure, the external energy sources may not be available and rendered the reactor kill system useless. Thus, a need exists for a mechanically driven safety injection kill system for protecting against vessel over pressurizations to replace or supplement existing traditional systems.
Note that throughout the following description, FIGS. 3a and 3b, though not directly referred to, can optionally be used to illustrate any reference to FIG. 1.